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Your search keyword '"ion thermal transport"' showing total 4 results
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4 results on '"ion thermal transport"'

1. Observation of a stationary double transport barrier in KSTAR

Author

M.W. Lee, S.-H. Hahn, D. Kim, J. Kang, W.H. Ko, J. Jang, W. Lee, and C. Sung

Subjects
internal transport barrier, edge transport barrier, ion thermal transport, ELM-free, KSTAR, Nuclear and particle physics. Atomic energy. Radioactivity, QC770-798
Abstract

We have observed a stationary high confinement regime with a double transport barrier (DTB), including both internal and edge transport barriers (ITB and ETB) but without edge-localized modes (ELMs), in KSTAR. The ELM-free DTB phase has high thermal confinement comparable to typical H-mode operation in KSTAR. We investigated the characteristics of the DTB phase through various analyses. Transport analysis shows a reduction of ion heat diffusivity to near neoclassical level after the transition from the ELMy H-mode phase to the DTB phase. This result supports the formation of an ion ITB during the DTB phase. Furthermore, we observed that the DTB phase had an edge thermal transport barrier in the ion temperature profile, comparable to that of the H-mode, without a particle transport barrier at the edge. Peeling-ballooning stability analysis indicates that a lower pressure gradient due to density decrease in the DTB phase is mainly responsible for the ELM-free operation. Linear gyrokinetic analysis shows that the real frequency of the most unstable mode in the core region ( ${\rho _{{\text{tor}}}}$ = 0.32–0.47) is in the ion diamagnetic direction at both H-mode and DTB phases. At the DTB phase, the linear growth rate inside the ITB is reduced by 50% compared to the ITB foot, while the reduction is not shown at the H-mode phase. Further investigation including nonlinear effects will be needed to better understand the unique operation mode, which can contribute to applying the physical mechanism to fusion reactors in the future.

Published
2024
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2. Carbon impurities behavior and its impact on ion thermal confinement in high-ion-temperature deuterium discharges on the Large Helical Device

Author

MUKAI, Kiyofumi, NAGAOKA, Kenichi, TAKAHASHI, Hiromi, YOKOYAMA, Masayuki, MURAKAMI, Sadayoshi, NAKANO, Haruhisa, IDA, Katsumi, YOSHINUMA, Mikiro, SEKI, Ryosuke, KAMIO, Shuji, Fujiwara, Yutaka, OISHI, Tetsutaro, GOTO, Motoshi, MORITA, Shigeru, MORISAKI, Tomohiko, OSAKABE, Masaki, LHD, Experiment Group, MUKAI, Kiyofumi, NAGAOKA, Kenichi, TAKAHASHI, Hiromi, YOKOYAMA, Masayuki, MURAKAMI, Sadayoshi, NAKANO, Haruhisa, IDA, Katsumi, YOSHINUMA, Mikiro, SEKI, Ryosuke, KAMIO, Shuji, Fujiwara, Yutaka, OISHI, Tetsutaro, GOTO, Motoshi, MORITA, Shigeru, MORISAKI, Tomohiko, OSAKABE, Masaki, and LHD, Experiment Group

Abstract

The behavior of carbon impurities in deuterium plasmas and its impact on thermal confinement were investigated in comparison with hydrogen plasmas in the Large Helical Device (LHD). Deuterium plasma experiments have been started in the LHD and high-ion-temperature plasmas with central ion temperature (T i) of 10 keV were successfully obtained. The thermal confinement improvement could be sustained for a longer time compared with hydrogen plasmas. An isotope effect was observed in the time evolution of the carbon density profiles. A transiently peaked profile was observed in the deuterium plasmas due to the smaller carbon convection velocity and diffusivity in the deuterium plasmas compared with the hydrogen plasmas. The peaked carbon density profile was strongly correlated to the ion thermal confinement improvement. The peaking of the carbon density profile will be one of the clues to clarify the unexplained mechanisms for the formations of ion internal transport barrier and impurity hole on LHD. These results could also lead to a better understanding of the isotope effect in the thermal confinement in torus plasma., source:Citation K Mukai et al 2018 Plasma Phys. Control. Fusion 60 074005, source:https://doi.org/10.1088/1361-6587/aac06c, identifier:0000-0003-1586-1084

Published
2021

3. Carbon impurities behavior and its impact on ion thermal confinement in high-ion-temperature deuterium discharges on the Large Helical Device

Author

Haruhisa Nakano, Katsumi Ida, T. Oishi, S. Morita, Sadayoshi Murakami, Masaki Osakabe, Y. Fujiwara, Kiyofumi Mukai, Ryosuke Seki, Masayuki Yokoyama, Kenichi Nagaoka, Motoshi Goto, Tomohiro Morisaki, Shuji Kamio, Hiroyuki R. Takahashi, and Mikiro Yoshinuma

Subjects
deuterium plasma, Materials science, Hydrogen, confinement improvement, chemistry.chemical_element, ion thermal transport, Thermal diffusivity, 01 natural sciences, 010305 fluids & plasmas, Ion, Large Helical Device, carbon impurity, particle transport, Physics::Plasma Physics, 0103 physical sciences, Kinetic isotope effect, 010306 general physics, Plasma, Condensed Matter Physics, Nuclear Energy and Engineering, Deuterium, chemistry, Physics::Space Physics, LHD, Atomic physics, Carbon, isotope effect
Abstract

The behavior of carbon impurities in deuterium plasmas and its impact on thermal confinement were investigated in comparison with hydrogen plasmas in the Large Helical Device (LHD). Deuterium plasma experiments have been started in the LHD and high-ion-temperature plasmas with central ion temperature (T i) of 10 keV were successfully obtained. The thermal confinement improvement could be sustained for a longer time compared with hydrogen plasmas. An isotope effect was observed in the time evolution of the carbon density profiles. A transiently peaked profile was observed in the deuterium plasmas due to the smaller carbon convection velocity and diffusivity in the deuterium plasmas compared with the hydrogen plasmas. The peaked carbon density profile was strongly correlated to the ion thermal confinement improvement. The peaking of the carbon density profile will be one of the clues to clarify the unexplained mechanisms for the formations of ion internal transport barrier and impurity hole on LHD. These results could also lead to a better understanding of the isotope effect in the thermal confinement in torus plasma.

Published
2018
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4. Ion Heating Experiments Using Perpendicular Neutral Beam Injection in the Large Helical Device

Author

Kenichi NAGAOKA, Masayuki YOKOYAMA, Yasuhiko TAKEIRI, Katsumi IDA, Mikiro YOSHINUMA, Seikichi MATSUOKA, Hisamichi FUNABA, Shigeru MORITA, Takashi MUTOH, Tetsuo SEKI, Katsunori IKEDA, Masaki OSAKABE, Katsuyoshi TSUMORI, Yoshihide OKA, Osamu KANEKO, and null the LHD Experimental Group

Subjects
Toroid, Materials science, charge exchange spectroscopy, toroidal rotation, ion heating, confinement improvement, ion thermal transport, Plasma, beam fueling, Condensed Matter Physics, Neutral beam injection, Ion, Large Helical Device, Ion beam deposition, perpendicular NBI, Physics::Plasma Physics, Atomic physics, Ion transporter, Beam (structure)
Abstract

A perpendicular neutral beam (P-NB) injector was installed in the Large Helical Device (LHD) and utilized for high-power ion heating and measurement of the ion temperature (Ti) profile by charge exchange spectroscopy. Significant progress was achieved in ion heating experiments using P-NB, and a high Ti of 5.2 keV was achieved at the plasma center. A Ti peak profile with a steep gradient in the core region was observed, indicating an improved mode of ion transport. The enhancement of toroidal flow in the core region was observed with the Ti rise. Transport analysis shows improvement in anomalous transport in the core region, and the neoclassical transport remains unchanged when the high Ti is realized.

Published
2008

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